I don't want to have to get a special purpose credential when I have a TGT which can work generally, and is at least required for secure remote filesystem access.
You have to manage extra infrastructure for certificates and, as a user, have the friction of firing up a JavaScript-enabled web browser via an additional tool, assuming "real IdP" means using OIDC. Unfortunately that flow is actually needed for remote systems and something like Edugain federation, since Moonshot/IETF ABFAB failed, but at least Shibboleth can use the TGT, and it's not the Globus horror.
You have to manage extra infrastructure for certificates and, as a user, have the friction of firing up a JavaScript-enabled web browser via an additional tool, assuming "real IdP" means using OIDC. Unfortunately that flow is actually needed for remote systems and something like Edugain federation, since Moonshot/IETF ABFAB failed, but at least Shibboleth can use the TGT, and it's not the Globus horror.